Coupling enhancement of split ring resonators on graphene

Cataloged from PDF version of article.Metallic split ring resonator (SRR) structures are used in nanophotonics applications in order to localize and enhance incident electromagnetic field. Electrically controllable sheet carrier concentration of graphene provides a platform where the resonance of the SRRs fabricated on graphene can be tuned. The reflectivity spectra of SRR arrays shift by applying gate voltage, which modulates the sheet carrier concentration, and thereby the optical conductivity of monolayer graphene. We experimentally and numerically demonstrated that the tuning range can be increased by tailoring the effective mode area of the SRR and enhancing the interaction with graphene. The tuning capability is one of the important features of graphene based tunable sensors, optical switches, and modulator applications. © 2014 Elsevier Ltd. All rights reserved

Resonance tuning and broadening of bowtie nanoantennas on graphene

Cataloged from PDF version of article.Metallic bowtie antennas are used in nanophotonics applications in order to confine the electromagnetic field into volumes much smaller than that of the incident wavelength. Electrically controllable carrier concentration of graphene opens the door to the use of plasmonic nanoantenna structures with graphene so that the resonant nature of nanoantennas can be tuned. In this study, we demonstrated with the Fourier transform infrared (FTIR) spectroscopy and the Finite Difference Time Domain (FDTD) method that the intensity and resonance peak of bowtie nanoantennas on monolayer graphene can be tuned at mid-infrared (MIR) wavelength regime by applying a gate voltage, since the optical properties of graphene change by changing the carrier concentration. (C) 2014 Elsevier B.V. All rights reserved

One-way reciprocal spoof surface plasmons and relevant reversible diodelike beaming

Cataloged from PDF version of article.One-way excitation of spoof surface plasmons (SPs) and strongly pronounced diodelike extraordinary transmission of linearly polarized waves in the beaming regime can be obtained by combining spoof SPs and cross-polarization conversion resonances. The reciprocal composite structure that is suggested to realize this mechanism consists of a symmetric metallic grating with a subwavelength slit and a metamaterial based ultrathin 90 degrees polarization rotator and, therefore, shows the broken spatial inversion symmetry. In contrast to the earlier studies of SP inspired transmission through subwavelength slits, asymmetric (one-way) beaming is demonstrated at normal incidence and for both s- and p-polarized incident waves. Furthermore, as an implication of Lorentz reciprocity, the studied diodelike mechanism is reversible, which manifests itself in that transmission is significant for one of the two opposite illumination directions at s polarization and for the other direction at p polarization. The obtained numerical and experimental results verify the general idea and enable us to select the optimal operation regimes

Validation of electromagnetic field enhancement in near-infrared through Sierpinski fractal nanoantennas

Cataloged from PDF version of article.We introduced fractal geometry to the conventional bowtie antennas. We experimentally and numerically showed that the resonance of the bowtie antennas goes to longer wavelengths, after each fractalization step, which is considered a tool to miniaturize the main bowtie structure. We also showed that the fractal geometry provides multiple hot spots on the surface, and it can be used as an efficient SERS substrate. (C)2014 Optical Society of America

One-way transmission through the subwavelength slit in nonsymmetric metallic gratings

Cataloged from PDF version of article.An approach for obtaining one-way transmission in the beaming regime is suggested that is based on the directional radiation of surface plasmons in nonsymmetric metallic gratings with a single slit. In contrast to the various nonsymmetric one-way diffraction gratings that have recently been proposed, the possibility of obtaining of narrow beams is demonstrated. Strong directional selectivity can appear a wide range of the observation angles, while the angle of incidence is retained. © 2010 Optical Society of Americ

Fano resonances in THz metamaterials composed of continuous metallic wires and split ring resonators

Cataloged from PDF version of article.We demonstrate theoretically and experimentally that Fano resonances can be obtained in terahertz metamaterials that are composed of periodic continuous metallic wires dressed with periodic split ring resonators. An asymmetric Fano lineshape has been found in a narrow frequency range of the transmission curve. By using a transmission line combined with lumped element model, we are able to not only fit the transmission spectra of Fano resonance which is attributed to the coupling and interference between the transmission continuum of continuous metallic wires and the bright resonant mode of split ring resonators, but also reveal the capacitance change of the split ring resonators induced frequency shift of the Fano resonance. Therefore, the proposed theoretical model shows more capabilities than conventional coupled oscillator model in the design of Fano structures. The effective parameters of group refractive index of the Fano structure are retrieved, and a large group index more than 800 is obtained at the Fano resonance, which could be used for slow light devices. (C) 2014 Optical Society of Americ

Spoof-plasmon relevant one-way collimation and multiplexing at beaming from a slit in metallic grating

Diode and collimator/multiplexer functions are suggested to be combined in one device that is based on a thin metallic grating with a single subwavelength slit. A proper choice of the structural (a)symmetry of the grating can result in obtaining one-way collimation and multiplexing with a single on-axis or off-axis, or two off-axis narrow outgoing beams. It is possible due to freedom in utilizing different combinations of the excitation conditions of the spoof surface plasmons at the four grating parts - right and left front-side and right and left back-side ones. Such a combining provides one with an efficient tool to engineer one-way collimators and multiplexers with the desired characteristics. Strong asymmetry in transmission with respect to the incidence direction (forward vs backward case) can be obtained within a wide range of variation of the incident beam parameters, i.e., angle of incidence and frequency, while the outgoing radiation is concentrated within a narrow range of the observation angle variation. Most of the observed asymmetric transmission features can be qualitatively explained using the concept of the equivalent source placed inside the slit. © 2012 Optical Society of America

Concentric ring structures as efficient SERS substrates

Plasmonic nanopatterned structures that can work as highly efficient surface-enhanced Raman scattering (SERS) substrates are presented in this study. A 'coupled' concentric ring structure has been designed, fabricated, tuned, and compared to an 'etched' concentric ring structure and plain gold film via SERS experiments. The proposed design gives Raman signal intensity 630 times larger than plain gold film and 8 times larger than an 'etched' concentric ring structure. The surface plasmons were imaged with the fluorescence imaging technique and supporting numerical simulations were done. © 1995-2012 IEEE

SiC substrate effects on electron transport in the epitaxial graphene layer

Cataloged from PDF version of article.Hall effect measurements on epitaxial graphene (EG) on SiC substrate have been carried out as a function of temperature. The mobility and concentration of electrons within the two-dimensional electron gas (2DEG) at the EG layers and within the underlying SiC substrate are readily separated and characterized by the simple parallel conduction extraction method (SPCEM). Two electron carriers are identified in the EG/SiC sample: one high-mobility carrier (3493 cm(2)/Vs at 300 K) and one low-mobility carrier (1115 cm(2)/Vs at 300 K). The high mobility carrier can be assigned to the graphene layers. The second carrier has been assigned to the SiC substrate